/Engine/Plugins/Experimental/Mutable/Source/CustomizableObject/Classes/MuCO/CustomizableObjectExtension.h
To create a new extension, make a subclass of this class and register it by callingICustomizableObjectModule::Get().RegisterExtension().
[UCLASS](Programming/UnrealArchitecture/Reference/Classes#classdeclaration)() class UCustomizableObjectExtension : public [UObject](API\Runtime\CoreUObject\UObject\UObject)